[FEAT] Gradients #427
Description
I just realized wo don't have gradients yet, which are really important to get a not-completely-flat-looking UI
I expect gradients to be relatively simple to implement across platforms, at least the simple ones.
Gtk might actually be the easiest due to CSS support.
The first gradients I would like to support initially are: LinearGradient, RadialGradient and AngularGradient.
Honorary mention of MeshGradient which would be nice to have as well.